138 



HANDBOOK OF INVERTEBRATE ZOOLOGY. 



is to form the integument of the upper surface of the body 

 of the starfish. The extremities of this band {ab^ and 

 aU', Fig. 80) are widely separated, and it is divided into 

 five lobes, corresponding to the five rays, each lobe being 

 again divided into four smaller lobes. 



The upper and lower surfaces of the future echinoderm 

 are thus seen to be on the right and left sides respectively 

 of the stomach of the larva. They include between them 

 part of the right water-tube, which is to become the body 



Fig. 82. 

 Fig. 82. — Ab-oral surface of very young starfish, 

 ture by E. B. Wilson. ) 



(Drawn from na- 



cavity of the starfish ; part of the stomach, which is to 

 become the digestive tract of the starfish ; and part of the 

 left water-tube, which is to become the water-system. 



d. The young starfish. 



These portions grow and fold towards each other ; a new 

 mouth is formed in the centre of the rosette on the left 



